Method and composition for preparing ferrous metal for forming



NiET-EGD AND C(TPMPGSITIQN FOR PREPARING FERRUUS METAL FGR FORMINGGilbert H. Grozco, Euclid, and Richard Roy, Cleveland, Ohio, assignors,by mesne assignments, to The Pennsylvania Salt Mmufacturing Co., acorporation of Pennsylvania No Brawing. Application March 3, 1950,Serial No. 147,564

9 Claims. (Ci. 1486.i5}

This invention relates to a method and composition for preparing ferrousmetal for forming operations such as die forming and stamping of sheetstock, cold heading, and drawing of wire, rod and tubular stock, and thelike.

As fully set forth in United States Letters Patent Reissue No. 23,184,reissued on December 29, 1949, to R. A. Whitbeck, it has been founddesirable in the forming of metal stock to dispense with the usual wetlubricants and instead to coat the stock with a dry, homogeneous,self-adherent, lubricating and protective film which is readilyremovable, then to form the coated stock, in the absence of anyadditional lubricant, and to remove the film from the formed stocl:after which the formed stock is ready for painting, plating and thelike. The film thus formed of alkaline material adheres to the stock dueto a mechanical bond.

On very smooth surfaces, such as bright cold rolled steel, bright finishstainless steel, and steel stock which has been polished and buffed,difficulty occasionally is encountered with draws of very sharp radiidue to a i tendency, in such instances, for the lubricating film toshear off of the stock along the areas of sharp radius and build up onthe dies. in due course, the lubricating material so built up on thedies sometimes causes a slight pattern on the steel and must be removed.

In such extreme cases the difficulty can be overcome by slightly etchingthe metal before coating with the lubricating film, or by coating themetal stock with a very thin porous coat which can be chemicallyremoved, so as to provide better mechanical adhesion with thelubrieating and protective film.

The advantages of this type of lubricating film and the procedures madepossible thereby are fully set forth in the above reissue patent.

The present invention relates primarily to a method and composition forproviding on the stock a chemically bonded microporous film by whichbetter adhesion of the lubricating and protective film is obtained.

The invention also relates to a method and composition by which there isprovided on the stock a microporous chemically bonded film which initself is lubricating and which can be removed readily from the stock,the stock being lightly etched and coated in a single bath with achemically bonded film containing sufiicient lubricant so that the stockcan be formed in the absence of any additional lubricant, thusdispensing with the need for the subsequent application of a lubricatingand protective film such as described in the above reissue patent.

Referring first to the provision of the chemically bonded microporousfilm, which in itself is non-lubricating, the metal to be treated isfirst cleaned in any suitable manner, such as by an alkaline bath or bysolvents, so that it is free from oleaginous material and other organicsoils. The cleaned stool; is then subjected to an aqueous bath of oxalicacid, phosphoric acid of 85% concentration, and hypophosphorous acid of50% concentration. An example of a very satisfactory bath which isuseful hired rates Patent throughout a wide range of operatingconditions and for a wide range of ferrous metals is as follows:

concentration) Hypophosphorous Acid about 1 part about 1 part.

(50% concentration). Water about 1,000 parts. about 250 to 5,000 parts.

Additional specific examples are as follows:

Example II For thin films:

Oxalic acidabout 10 parts Phosphoric acidabout 10 parts Hypophosphorousacid about 1 part Water-same as in Example I.

Example III For thick films:

Oxalic acidabout 25 parts Phosphoric acid-about 5 parts Hypophosphorousacidabout 1 part Watersame as in Example I The ferrous stock issubjected to the aqueous solution by dipping or the like forapproximately three minutes with the solution at a temperature from 200to 205 degrees Fahrenheit. The reaction of the bath on the metal is veryrapid for about one to one and one-half minutes and thereafter graduallydecreases, becoming negligible at the end of three minutes. As a resultof this treatment there is formed on the stock a microporous film whichis chemically bonded to the metal.

The above example is one particularly suitable for bright cold rolledsteel and high finish stainless steel but the example is not inlimitation of the composition, proportions, or method, as widevariations may be made in each depending upon the type of ferrous metal,the alloying ingredients, the amount of impurities in the metal, thetype of surface desired in the finished article, and the time factorwhich may be dictated by other procedures in the particular plant.

In order to inform others how to vary the composition and the method ofapplication for the particular results desired and for bettercoordination with their existing practices, the function of theingredients and the changes resulting from variations in theproportions, concentrations and the like are now pointed out.

The oxalic acid appears to react with the iron to form an iron oxalatefilm which is bonded chemically to the stock. The phosphoric acid etchesthe steel, thus assisting in the formation of the oxalate film andassuring an effective bond. The hypophosphorous acid is used as anaccelerator, accelerating both the etching action and the film formingaction.

Further, from the examination of the resultant film, it appears that thephosphoric acid probably cooperates with the oxalic acid to produce aniron phospho-oxalate film. cally bonded to the surface of the stock.

After the treatment in the manner described, the stock is ready for theapplication of coatings, such as lubricating coatings, and for drawingin lubricated 0011- dition. As a lubricant, it is preferred to use thelubricating and protective coating described in the above reissue patentbut other lubricants may be used as the microporous structure of thefilm retains the lubricant in place.

In any event the film is microporous and chemi- As the proportion ofoxalic acid is decreased the rate of formation of film is decreased. Asthe oxalic acid is increased the rate of film formation is increased andthis increase can proceed to such an extent that the rate of filmformation is so disproportionate to the rate of etching that thefilmtends to become powdery and insufficiently adherent.

As the phosphoric acid is decreased the rate of etching of the metal isdecreased and this likewise can result in an improper balance betweenetching and film formation. As the phosphoric acid is increased tue rateof etching is increased and, unless there is a sufiiciently highconcentration of oxalic acid, the metal surface becomes etcheddisproportionately and to too great a degree before a suificient film isformed.

An increase in the concentration of the soluble ingredients in the bathresults in faster reactions whereas a decrease in the concentrationslows down the reactions.

As the proportion of hypophosphorous acid is decreased, all reactionsare slowed down and the time factor becomes controlling. In fact,without an accelerator an impractically long time is required. Anincrease in the accelerator results in a waste of the acceleratingmaterial.

In general, for a given type and thickness of film for a given ferrousmetal, if the amount of oxalic acid is increased, the phosphoric acidlikewise should be increased proportionately so as to maintain a balancebetween the rate of etching and therate of film formation for theparticular stock.

The concentration of these ingredients and their proportions dependslargely on the type of steel or steel alloy, the kind of etch and thetype of film desired. For example, in some metals a light etch with arelatively heayy film might be desirable whereas in others a heavieretch with a lighter film may be desirable and all degrees of relationsbetween the type of etch and type or" film may be obtained.

lfa much more concentrated aqueous bath is employed, for example, about250 parts of water instead of 1,000 parts with the amount of solubleingredients remaining the same as described heretofore, the bath worksefiectively but since the bath becomes contaminated with iron due to theflocking of the iron, an unduly concentrated bath results in a waste ofchemicals with no appreciable ofisetting benefits. In fact, the moredilute the bath can be while still providing the desired film and etch,the better.

If the amounts of soluble ingredients remain the same and the water isincreased to about 5,000 parts, there is a very rapid drop in the ratesof reactions and too much time is required for obtaining the results.Preferably, therefore, with the other ingredients remaining in about theamounts recited in the example, water in an amount from about 800 to1200 parts is preferred.

In general the phosphoric acid should be used in a proportion'of notless than about 1 partof phosphoric acid to 5 parts of oxalic acid andnot more than about 1 part of phosphoric acid to 1 part of oxalic acid.The hypophosphorous acid is preferably kept in about the ratio of 1 partto parts of phosphoric acid.

Instead of oxalic acid, zinc phosphate or zinc oxalate or combinationsthereof may be used for all or part of the oxalic acid. When either isso used, it should be substituted for the oxalic acid in the rangesrecited in'the ratio of about 3 parts of zinc phosphate or oxalate for 5parts of oxalic acid.

Thus, films satisfactory for many purposes can be formed by subjectingthe ferrous metal to an aqueous acid bath of material which, in theaqueous acid bath, reacts with the iron to produce complex ironcompounds which are insoluble in the bath.

If it is desired to provide not only a microporous chemically bondedfilm but a film which in itself is lubricating the same procedure asused above may be folfill ' the same as that used for non-lubricatingfilms.

of the phosphoric acid.

all.

lowed except that there is added to the bath a lubricant which isnon-reactive with respect to the bath. The lubricant preferably is one,or a combination of two or more of the acid soluble esters of complexalcohols such, for example, as polyethylene glycol phosphate, glycerolborate, glycerol phosphate, and glycol borate.

More specifically, the esters may be acid-soluble aliphatic polyhydricalcohol esters having less than four hydroxy groups of inorganic acids.

The polyethylene glycol phosphate is preferred. If one or more of theselubricating ingredients is used wi h polyethylene glycol phosphate, thelatter should be at least about onehalf of the. total of the esters.

Thus the lubricant may be polyethylene glycol phosphate and one or moreof the group consisting of glycerol phosphate, glycerol borate, andglycol borate.

if the polyethylene glycol phosphate is not employed, there is atendency toward tackiness of the resultant film and a moist filmresults. However, metallic salts or" iron, manganese, Zinc, lead and thelike may be added so that the film can be dried. The salts are added inan amount equal to about one-fourth of the amount of phosphoric acidemployed in the bath.

The procedure with the bath for lubricating films is The coated stockmay be drawn while the film is only partially dry or fully dry. Whenfull drying is required after subjection of the metal to the bath, thedrying time is varied, depending upon the particular lubricating effectdesired. If the lubricant to be added is polyethylene glycol phosphate,it is readily obtained as follows: A polyethylene glycol,(OHCH2(CH2OCI12)$CHOH), such as is readily available on the market underthe name Carbowax 4000 or Carbowax 6000, which is solid at roomtemperature is melted. To this melted polyethylene glycol there is addedphosphoric acid at concentration, these two ingredients being in theratio of about parts of polyethylene glycol to about 5 parts Thismixture is then heated to about 350 degrees Fahrenheit for about 30minutes, after which is allowed to cool. As a result a solid hard waxymaterial is obtained and appears to be a polyethylene glycol phosphate.To the bath heretofore described, from about 5 to 15 parts, preferablyabout 10 parts, of this material is added. Thus a satisfactory bathwould comprise:

concentration) Hypophosphorous acid (50% concentration). Polyethyleneglycol phosphate. Water about 1 part about 10 parts..-

about 1,000 parts about 1 part.

about 5 to 15 parts.

about 250 to 5,000 parts.

As the amount of the lubricant is decreased, the lubricity decreases. Asthe amount of the lubricant is increased, the lubricity increases andthe film gradually tends to, and finally becomes, tacky. The stock maybe exposed in the bath for about 3 minutes at a temperature of about 200to 205 degrees Fahrenheit after which it is removed. It may be drawnwhile the film is moist and partially dry or fully dry. In faces wheredrying is desired, for very thin films, drying at about 200 to 205degrees Fahrenheit is satisfactory and for thicker films, of

. the same type, the coated stock should be dried at the sametemperature but for a longer time. The resultant film is slippery,highly tenacious. It has no tendency to build up on the dies at sharpradii under the heat of forming.

By drying at a temperature of 400 to 450 degrees chemical change in themetallic film itself. Possibly this is due to change of the compoundfrom a ferrous to a ferric state, that is, the changing of the film froma ferrous phospho-oxalate to a ferric phospho-oxalate, which latter ismuch more stable. At least it is known that if like pieces of stock arecoated in the same manner and one is dried at 200 to 205 degreesFahrenheit and the other at 400 to 450 degrees Fahrenheit, the resultantfilm on the latter is harder to break down and remove both mechanicallyand chemically than the former.

In any of the above examples, some additional substitutions can be made.For example, hydrogen fluoride may be substituted in whole or part foroxalic acid but in the examples given the hydrogen fluoride would besubstituted in an amount of about one part of hydrogen fluoride for fiveparts of oxalic acid. If hydrogen fluoride is used to the exclusion ofoxalic acid, etching only is obtained. Since this substitute formulaprovides a deeper etch the rough surface of the metal is depended uponfor holding a subsequently applied lubricating film. It does not providea chemically bonded film. Such is desirable for etching high siliconsteels.

Where combined etching and microporous film is desired some oxalic acid,Zinc phosphate or zinc oxalate, or combinations of two or more thereofmust be added. In those instances wherein both the etch and microporousfilm are to be obtained, the metal may be exposed in the solution untilthe reaction runs to completion without deleterious effects.

In connection with all of the above compositions and procedures, afterforming or drawing the stock, the film is removed by dipping the stockin a strong aqueous acid solution employing inorganic acids after whichthe formed stock is rinsed and dried.

Where the word parts has been employed herein- A material selected fromthe group consisting of oxalic acid, zinc oxalate, and zinc phosphate,and mixtures of the foregoing Acid-soluble, aliphatic polyhydric alcoholester having less than four hydroxy groups of an inor- About 5 to parts.

ganic acid Phosphoric acid (about 85% concentration) About 5 to 15parts.

and Hypophosphorous a c i d (about 50% concentration) About 1 part.

2. A composition according to claim 1 characterized in that said esteris polyethylene glycol phosphate.

3. A composition according to claim 1 characterized in that the ester isat least one material selected from the group of glycerol phosphate,glycerol borate, and glycol borate.

4. A composition according to claim 1 characterized in that said esteris a mixture of polyethylene glycol phosphate and at least one esterselected from the group consisting of glycerol phosphate, glycerolborate, and glycol borate.

5. A composition according to claim 3 characterized in that thepolyethylene glycol phosphate is at least about one-half of the totalester.

About 10 to parts.

6. A composition to be dissolved in water to provide an aqueous acidbath for applying to ferrous metal stock to form thereon a microporouslubricating film which is chemically bonded to the stock and consistingessentially of the following:

Oxalic acid About 10 to 30 parts. Phosphoric acid (about concentration)About 5 to 15 parts. Hypophosphorous acid (about 50% concentration)About lpart.

and Polyethylene glycol phosphate About 5 to 15 parts.

7. A composition to be dissolved in water to provide an aqueous acidbath for applying to ferrous metal stock to form thereon a microporouslubricating film which is chemically bonded to the stock and consistingessentially of the following:

Oxalic acid About 25 parts. Phosphoric acid (about 85% concentration)About 10 parts. Hypophosphorous acid (about 50% concentration) About 1part.

and Polyethylene glycol phosphate About 10 parts.

8. The method of providing on ferrous metal stock a microporouslubricating film which is chemically bonded thereon and comprisingsubjecting the stock to a hot aqueous acid bath consisting essentiallyof about 5 to 15 parts of phosphoric acid, about 1 part ofhypophosphorous acid, about 10 to 30 parts of a material selected fromthe group consisting of oxalic acid, zinc oxalate, and zinc phosphate,and mixtures of the foregoing, and about 5-15 parts of an acid-soluble,aliphatic, polyhydric alcohol ester having less than four hydroxy groupsof an inorganic acid, and which is non-reactive to said bath,maintaining the stock subjected to the bath until the desired film isformed, then removing the stock.

9. The method of providing on ferrous metal stock a microporouslubricating film which is chemically bonded thereon and comprisingsubjecting the stock to a hot aqueous acid bath consisting essentiallyof about 5 to 15 parts of phosphoric acid, about 1 part ofhypophosphorous acid, about 10 to 30 parts of a material selected fromthe group consisting of oxalic acid, Zinc oxalate, and zinc phosphate,and mixtures of the foregoing, and about 5 to 15 parts of anacid-soluble, aliphatic, polyhydric alcohol ester having less than fourhydroxy groups of an inorganic acid, and which is non-reactive to saidbath, maintaining the stock subjected to the bath until the desired filmis formed, then removing the stock and drying the stock at a temperatureof from about 400 to 450 degrees Fahrenheit.

References Cited in the file of this patent UNITED STATES PATENTS1,315,017 Gravel] Sept. 2, 1919 1,485,025 Green Feb. 26, 1924 1,525,904Allen Feb. 10, 1925 1,610,362 Coslett Dec. 14, 1926 1,895,569 CurtinJan. 31, 1933 1,911,537 Tanner May 30, 1933 2,008,939 Tufts July 23,1935 2,080,299 Benning May 11, 1937 2,105,015 Singer Jan. 11, 19382,164,042 Romig June 27, 1939 FOREIGN PATENTS 707,865 Germany July 5,1941

1. A COMPOSITION TO BE DISSOLVED IN WATER TO PROVIDE AN AQUEOUS BATH FORAPPLYING TO FERROUS METAL STOCK TO FORM THEREON A MICROPOROUSLUBRICATING FILM WHICH IS CHEMICALLY BONDED TO THE STOCK AND CONSISTINGESSENTIALLY OF THE FOLLOWING: A MATERIAL SELECTED FROM THE GROUPCONSISTING OF OXALIC ACID, ZINC OXALATE, AND ZINC PHOSPHATE, AND MIXTUREOF THE FOREGOING-----ABOUT 10 TO 30 PARTS. ACID-SOLUBLE, ALIPHATICPOHYDRIC ALCOHOL ESTER HAVING LESS THAN FOUR HYDROXY GROUPS OF ANINORGANIC ACID------------------ ABOUT 5 TO 15 PARTS. PHOSPHORIC ACID(ABOUT 85% CONCENTRATION)----------------- ABOUT 5 TO 15 PARTS. ANDHYPOPHOSPHOROUS ACID (ABOUT 50% CONCENTATION)---------- ABOUT 1 PART